jse

I think Peter's got it. I'll try to do a quick-and-dirty, overslimplified technical answer as to gear design and function: There are basically two patterns in gear profiles, helical and straight-cut, and each has it's positive and negative points. Design Engineers will choose the pattern according to the gear's proposed use. Helical profile: nice and quiet (used a lot in various street bikes) as there is more than one tooth engaged with the corresponding gear it works with. If you look closely at engaged helical gears, you'll notice that in addition to the primary tooth contacting the corresponding gear tooth it works with, the teeth on either side of the primary tooth are partially contacting the teeth of the gears on either side of the corresponding gear tooth. The negative aspects of helical gears is that there is a lot of friction involved due, in part, to more surface area in contact. Another very big power robber is that the gear sets are always trying force each other apart sideways (they are like opposing screw drives, and exert a lot of side force) and the shaft bearings have to deal with a lot of pressure in two directions, up and down and left and right. Straight-cut profile: Good for transfering motion/energy with minumum power loss, but due to primarily one tooth at a time in contact (there is some secondary tooth contact) they can be noisey. As there is little side force, frictional losses are at a minumum and shaft bearings deal with mainly uni-directional pressures. The main reason the gears seem louder at idle (besides the exhaust audio pulses reduced) is that the crankshaft is not rotating at a constant rate. With the negative pressure on the crank pin (BTDC) caused by the piston compressing the fuel/air mixture, the crank is momentarially slowed down. With combustion pressure exerting positive force on the crank pin (ATDC), the crank is sped up. So you have the opposing pressures forcing the engaged teeth back and forth against each other, and at idle the pulses are farther apart (low RPM), which exacerbates the rattle. It's actually more complicated than my long-winded explanation (there are other minor factors to consider, but tooth design seems to be the major one from my experience), but I hope it made some sense. As Trials bikes are essentially full on competition motorcycles (and idling in neutral is a small part of their day), the design engineer's choice of putting up with a little rattle at idle to gain increased performance under competition conditions seems reasonable. The lightweight Pro engine, with it's lack of extra mass to absorb internal "noise" is more prone to the idle-rattle syndrome. When you pull in the clutch lever, frictional drag is introduced into the system, therefore the noise is lessened due to the damping effect on the contact/no-contact situation with the gear teeth. Jon, as usual, TMI.....

A common way is to back out the brass plug in the center of the pump (with the Torx recess, it's also the bushing that the water pump shaft rides in). Pull the tank and loosen the radiator cap first, or it can gush out if there is any pressure in the system. Be careful unsnaping the spring clips on the clamps (they are reusuable) and a small, thin screwdriver seems to be effective. I use a 50/50 mix of automotive anti-freeze and distilled water and it has worked well, even in my Magnesium engine. Jon

Although I don't have the thread/pitch spec.'s right at hand, it's the same as the very common standard Japanese fine thread pullers for a majority of the two-stroke MX bikes. The kicker is that the GasGas is a right-hand thread and the standard Japanese flywheel puller is a left-hand thread. They look exactly the same, and I'm sure a lot of riders (including myself before I marked them so as to not grab the wrong one) have been quite puzzled why it wouldn't screw in correctly. I haven't found any other flywheel hub that uses that exact puller other than the GasGas. Jon

Jan, Darn, that serves me for guessing! I just looked at the parts manual and it seems to show the seal with the open side to the crank (it's tough to make out by the drawing). Goes to show you, I'm not too old to learn..... Actually, it makes some sense to me now after looking at the seal lip structure, as the pressure side (open) would tend to seal better with the pressure fluctuations, kinda like how shock absorber seals are designed to seal under pressure. Cheers. Jon

Stork, If done correctly, it would pinpoint the leak, as part of a leak-down test is to spray a soapy solution on the suspected areas to find out just where it's leaking. Jon

Geez, I'm trying to remember, but in my experience, the "open" side goes towards the side that contains the fluids. Think about the kickstart and shift shaft seals, open side goes towards the trans fluid, and I would think the open side goes towards the bearings, which are lubed by the transmission fluid. Any help? Jon

Excellent! I'm glad she is getting the recognition she deserves. Quite an honor! For those that are not familiar with the Taurus Awards, I found the following: "In the tradition of Hollywood's finest awards presentations, the best stunt men and women in the entertainment industry are recognized for their extraordinary performances with the Taurus World Stunt Awards. The Taurus World Stunt Awards are a vision of Red Bull Energy Drink and its founder, Dietrich Mateschitz, whose appreciation for stunt professionals has also inspired him to establish the Taurus World Stunt Awards Foundation. All proceeds from the awards show and related fundraising activities will help perpetuate the Foundation's grant fund, which is dedicated to the support of stunt performers in need." Jon

Yes!, yes we are! I know we can do it! And, as oldest member of the Diagnostic Triumvirate, I'll cheer the other two on and keep track of their lap times! If I had the engine in my shop, one of the first things I'd do is a leak-down test to determine the soundness of all the sealing devices. One of the common places for a two-stroke, case-reed engine to leak is under the manifold part of the case just above the top of the trans part of the case. I've seen missing gaskets and pinholes in the casting there and it's really hard to see the telltale oil spot that usually shows up with leaks of that type. What makes me think that a leak is, at least, partially to blame for the problem is the oft mentioned pinging ("pinking" in the UK). Unless there are unusual circumstances, like a clogged radiator for instance, a well-tuned engine, from my experience, should not ping. Pinging is the symptom of a problem with the combustion process and that generally means that some part of the engine/ignition/induction system is not doing the job as designed. Although it may not be fesible depending on what's available where you live, but any good two-stroke mechanic should be able to test the engine for you. Jon

J, There is the possibility that the clutch may need replacement or at least, an adjustment to the clutch pack width (it may be 7 years old) and if you measure the clutch finger height, that would be a good indicator. As the fiber plates wear, the pack width is reduced, which will lessen the preload on the spring. In rare instances, the fingers will extend far enough up that the servo cylinder will not be able to retract far enough to not put pressure on the fingers, and with the lessened spring pressure, will cause slippage. I'd check the pack width first. Bleeding a hydraulic system (unless done after parts replacement) usually only treats the symptom, not the cause. As far as I can figure, air in the line would contribute to clutch drag and not slippage. Jon

A couple of things to check: 1. Fork alignment (do the least expensive stuff first). Loosen all the fasteners except for the upper tripleclamp capscrews (axle, axle pinch bolts, lower tripleclamp capscrews and take off the fender brace). Push on the forks to "center" them and tighten the lower tripleclamp bolts. Again center the forks and tighten the axle. Center and tighten the axle pinch capscrews. Install the fork brace, and if the holes do not align with the mounts on the lower tube, file the holes so that the capscrews drop in. If this does not cure the problem, then do: 2. The mechanical condition of the forks. Make sure that the tubes are not bent by rolling them on a large flat surface, like a table top and seeing if there is a gap that appears between the tube and the surface (much better is two v-blocks and a dial indicator, but this will give you a rough measurement). Inspect the bushings, which are the grey Teflon coated collars on the bottom of the tubes and inside the inner part of the lower legs. If the coating is worn off at all, replace them. Make sure the rod in the center of the tubes (the cartridge rod) moves easily inside the cartridge. Chances are that your forks are good, but are binding somewhere and they can be fixed, don't worry about needing new forks. If you're a little concerned about making a mistake, I'm sure you have a buddy that, with the promise of a pint, will be glad to look over your shoulder while you search for the solution. I think the 99' has the three-piece lower fork leg, but they are basically the same as the later model GasGas forks and work well when properly adjusted. I don't know your weight, but some added preload may also help. Jon

Andy, The sprocket seal can often be carefully levered out without splitting the cases. Jut be very careful not to scar the surfaces where the oil seal lips ride. A large, long socket can be used as a seal installer, just tap lightly and don't try to move it too much at a time so it goes in straight. Jon

Steve, For a first-timer on silencer packing, the easiest way is with a loose-type packing like SilentSport. Don't pack it too tight, just read the directions. Some of us do the "cut, form and fit" packing with sheets of glass fibers, but that will be a pain if you have not done it before. Trials silencers are not round like a lot of the MX ones, so you can't just roll a sheet on ther core tube and stuff it back in. For the spring, I'd put the bike on a stand, spin the collar up to take up the slack on the spring and then spin the collar on about 10mm more for preload and set the jam spring to lock them together, try to be careful, adjustment collars are somewhat delicate and can be buggered up easily. Then, try the bike and adjust more or less preload till you get it where it gives the damping/springing you want. There is no "one-size-fits-all" for suspension settings. Cheers. Jon

Ishy, There were not many Trials riders up in the Shasta area when I lived in Northern California 10 years ago, but the potential is certainly there as there are a huge bunch of Cross Country and Enduro riders. The Shasta area has hosted a lot of top level off-road events in the past. The off-season use of ski areas for motorcycle events has been well proven as successful, for example Donner Ski Ranch and Mammouth Mountain MX series, and it gives the ski area owners a source of income in the warm months. The facilities are generally perfect for Trials as they usually have, like Donner, a big parking area and lodge. I hope they are able to get something going, it sounds like a great place to ride. Jon

They are not in production as yet. A new engineer from France is involved and they are making some changes to things such as valve size and acuation mechanism. I understand the RPM limit has been raised and they should have more than enough power and torque to tackle just about any obstacle. We're still waiting for a testing prototype here in the U.S. which should arrive soon. As other manufactuers have found, you want to get it right the first time on a totally new engine. Sherco had initial problems with their 4T that gave it an undeserved bad rep for several years and I'm glad that their four-stroke is making a comeback, it's a good design. I know how much blood, sweat and tears is put into introducing a new bike, so I'm happy to wait my turn on the buyer's list for a new one until they are satisfied with the results. Jon

Darn, I was hoping it was an easy fix. Looks like one or both of the inner seals is leaking. Unlike most two-strokes, you can suck trans oil from either side on a Pro as the crank mains are lubed by the trans fluid. In rare instances, an ill fitting case gasket will also allow trans fluid to enter the crank area, so carefully check all the case sealing surfaces to be sure there isn't a burr that keeps the case halfs from coming together completely. The area that seals on the cases is often only about 4mm wide. Good luck! Jon

Tire pressures, like brand of beer or pickup truck, is a very personal thing, so you will get a lot of variables. We have a certain amount of rocks where I ride (which is, for a Trials rider, a good thing as they are BIG rocks) and I usually run 6 PSI front and 4 PSI rear. Be sure to get a low pressure gauge, probably a 0-30 PSI max, and a 0-15 PSI is better. The standard 0-100 PSI gauges, even the good ones, usually have a minimum 2% +- callibration, so you can be 2 PSI off, not a big problem for a 44 PSI truck tire, but not good for a 4 PSI Trials tire. Jon

I don't know of any seller that will post to Australia around here, but I'm pretty sure you will want the Boyesen #651 set, if that's any help. Jon

The two-step proceedure I find that works well to reduce stalling in any Trials bike is: 1. Set the fuel/air mixture screw by (after warm-up) quickly blipping the throttle from idle and adjust the fuel/air screw in or out to get the best quick response. Each engine is different and there is no "right" setting for all engines. You should do this once in a while to adjust for the normal changing weather conditions. 2. Put bike in gear, and hold the clutch lever the way you would while riding (usually one finger holding lever to knuckles) and then adjust the tickover speed for section riding (usually just slightly higher than normal). This will compensate for any clutch drag. Jon

Jan, When working with cars, the "code" for smoke is, white=coolant, blue=oil and black=over-rich fuel mixture. I find bikes to be a little more difficult and sometimes it's a little hard to really tell what the smoke color is, so we look for other things such as, if the coolant level goes down or if the transmission level goes down. If the transmission fluid level was dropping, it probably is the right side crank seal leaking. If the coolant level was dropping, it most likely is the inside head o-ring leaking. These are probably the first things to check for a start. Jon

Neo, I also use Castrol TTS (at 70:1) and find it keeps the chamber quite clean, so I doubt that premix oil is the cause. Keep us up on what you find out, you have a very interesting problem and I'd sure like to know the final cause. Cheers. Jon

That's a good tip to lower the ramp and I don't see any reason it shouldn't work as well as a new black tube type (and the price is right). Jon

Dripping sarcasm aside, the possibility exists that no one on the forum has had the experience of using the Vapor on a Trials bike. The speedo assembly is one of the first things we take off our bikes here in the U.S. as they are usually only good for breakage in a get-off. Jon

Neo, What brand/type of premix oil is used? Make sure the throttle is wide open, the plug is properly grounded away from the plug hole and rapid, strong kicks for accuracy, usually 5 or 6 is enough. Yea, the "wandering mixture" is the weird thing about the problem. It's kinda like an infrequent misfire, they're the ones that will drive a mechanic nuts, as it's hard to pinpoint the related possibilities at the time the symptoms occur. Once you're established the symptoms, you look for patterns and relationships to follow the path to the cause. Most bike problems have a consistancy of effect-occurance, like leaking main seals, or manifold leaks, or chipped gears etc. so it's pretty easy to track, but something that reverses, like rich to lean mixture, exhibits opposite effects and sometimes one has to look for causes "outside the box". Jon

Interesting thread! A conundrum wrapped in an enigma you might say, and it took a while to follow through to the end...... I think the presenting issue was: "The air mixture is continually varying too rich, too lean, too rich, too lean, too rich, too lean!!!!...but is getting leaner and leaner and the airmix screw (on the PWK28mm) is hitting the stop now", I may ask, what exactly are all the observable/felt symptoms/under what conditions, that lead to the diagnosis? That might be a good place to restart. I think Stork mentioned the 215 PSI cranking pressure as being a little too high and a decoke might be needed (probably in the headpipe also), and I tend to agree that should be looked at. Although unusual in this age of full-synthetic premix oils, the buildup of carbon in the combustion chamber can cause various problems, such as elevated octane requirement. Compression cranking pressure (not totally related to compression "ratio", which is a mechanical measurement, and in racing two-strokes is usually measured as the ratio of the cylinder volume from the closing of the exhaust port by the piston, to the volume of the combustion chamber at TDC-this is referred to as "corrected compression ratio") that is too high can cause sometimes unsurmountable problems with carburation. Jon